The use of ballistic flying bodies such as non-guided rockets or projectiles fired from a gun regains increasing importance. For the precise delivery of a ballistic flying body such as a rovket or a projectile fired for example from an aircraft, it is necessary that the ballistic and the point of impact are ascertained. The impact point is dependent on a multitude of parameters such as attitude, position and motion status of the system from which the ballistic flying body is delivered. Additionally, the impact point is influenced by wind conditions and further characteristic values which relate to the rocket or projectile itself.
Several methods are known for determining the impact point. For example, the determination of the ballistic can be performed in that ballistic coefficients or parameters are determined ahead of time and then stored in the on-board computer of the aircraft in the form of ballistic tables. In accordance with the instantaneous system status a polynomial fit or a direct reading of the table values takes place when the weapon is used.
The above method permits, however, only a mission according to the predetermined coefficients, since the polynomial fit is based on these input values or because a direct reading only yields these values. Additionally, the required memory capacities become very large and even if the data matrix has a fine design only quantified solutions are obtained. Due to the quantified solutions the result is frequently rather imprecise. Moreover, the determination of the coefficients is very expensive. Another disadvantage lies in that the scene of the target must be completely ascertained. When an unforeseen target scene is involved, respective new ballistic tables are required, which calls for a large investment of time for the preparation of the mission.
For example, U.S. Pat. No. 4,494,198 (Smith et al.) discloses a weapons control system with a computer which comprises a first memory with convertible data for the shot distances and a second memory with correction coefficients correlated to different types of ammunition. A ballistic standard range is shown on a display. The standard range is combined with a correction factor in order to provide a corrected ballistic range.
U.S. Pat. No. 4,111,382 (Kissinger et al.) describes an apparatus for controlling a ballistic flying body in which the nominal or rated trajectory is compared with the actual flight parameters which are obtained by an inertia guidance system. A precise ballistic flight is achieved by way of a correction.
In another known method for determining the ballistics and ascertaining the point of impact, a model with three degrees of freedom is established from the actual system parameters. The term "degrees of freedom" as used herein means projectile or rocket intrinsic parameters and firing system parameters in a respective parameters model. Such parameters may include, for example, the mass center of gravity of the projectile, aerodynamic drag of the projectile and so forth. System parameters may include a helicopter downcast parameter, wind parameters and so forth. System parameters may include a helicopter downwash parameter, wind parameters and so forth. It is customary to also refer to these parameters as coefficients. In order to achieve a sufficient precision it is necessary to introduce correction factors at the beginning of the calculation. Particularly for complicated bodies, such as rockets, a multitude of correction factors are required within the model coefficient. The determination of the correction factors is very expensive and permits, just as with the above described method, only a mission based on discrete system states. Especially in connection with a rocket which is fired from a helicopter, larger interfering terms or conditions occur due to the downwash of the rotor. These interfering terms can only be corrected by respective correction factors in the three freedom degree integration model in a quantifying manner.
In order to increase the precision, it has been tried to determine the ballistics and thus the impact point by means of a six-coefficient or parameter model having 6 degrees of freedom. In such a method the flight path and the impact point are determined on the basis of six weapons specific characteristic parameters or coefficients. However, that method is very time consuming and it requires a very high computer capability. As a result, the method leads, on a mission where actual system states are involved, to time delays and thus to substantial imprecisions, especially when used in aircraft, such as combat aircraft or helicopters.